In conventional brushless DC motors the net flux is essentially dictated by the permanent magnets. The flux may be controlled to some extent by very large stator currents. This, however, is expensive in inverter rating and in energy,
It would be desirable to achieve a permanent magnet motor in which the flux may be controlled in a manner similar to that of an induction motor while retaining most of the desirable characteristics of the surface magnet (brushless DC) motor.